Photosensitive material



United States Patent 3,305,365 PHOTOSENSlTIVE MATERIAL Tomoshichi Takei, Masakazu Kanoh, and Shoichiro Sumi, Tokyo, .lapan, assignors to Oriental Photo Industrial Co., Ltd, Tokyo, Japan, a corporation of Japan No Drawing. Filed Nov. 8, 1963, Ser. No. 322,503 Claims priority, application Japan, Nov. 12, 1962, 37/ 49,678 Claims. (Cl. 96-108) This invention relates to photosensitive materials, especially to direct visual type electromagnetic oscillographic recording paper. More particularly the present invention relates to a photographic material which is photodevelopa-ble, is high in contrast and image stability, does not change during preservation, does not cause any latent image regression and is thus adapted to oscillographic recording.

As well known, when a silver salt photosensative material composed mostly of a silver halide is exposed to the sun light or an artificial light, the silver halide will produce a latent image which will be gradually developed to become black. However, when the exposed part having received the light and the unexposed part having received no light are to be distinguished from each other without chemical developing and fixing operations, the blackening phenomenon will occur in a short time. The blackness will increase with the lapse of time until there is no contrast with the exposed part and both parts will thus become so black as to be unable to be distinguished from each other. However, as a photosensitive material adapted to oscillographic recording, there has recently been developed a material having a silver halide emulsion layer which need not be treated in a darkroom or under a safety light and does not require such complicated and time consuming operations as chemical development and fixing, water-washing and drying treatments and which, when exposed to the light of a source of strong illumination as, for example, of a very high pressure mercury vapor lamp under a dry state, will make a latent image which can be developed to be a visible image when further exposed to the secondary light of a source of weak illumination as, for example, of a fluorescent lamp or the diffused ambient sun light. Such emulsion adapted to photographic recording and oscillographic recording can be exposed at a high speed and requires no chemical development.

A silver halide emulsion containing at least 0.5 mol percent of a stannous salt and at least 0.1 mol percent of a plumbous salt per mol of silver and halogen ions in excess of the equivalent of silver has been suggested as a photodevelopable direct visual type recording emulsion. The combination of the stannous salt and plumbous salt with a photographic silver halide emulsion containing excess halogen ions is superior to an emulsion containing only the stannous salt or having no excess halogen ions and any other previously suggested silver halide emulsions both in the stability with the lapse of time and in the contrast of the oscillographic image recorded at a low writing velocity. Further, also according to our study in the direct visual type oscillographic photographic emulsion, as the image is developed by utilizing the photographic developing eifect of the secondary exposure with a fluorescent lamp or the diffused ambient sun light after the primary exposure, for example, with a very high pressure mercury vapor lamp, the above mentioned developing action to obtain a visible image from the latent image is so weak that, in order to obtain an effective functional effect, the method wherein comparatively large amounts of the stannous salt and plumbous salt are added to the photographic emulsion in addition to the excess halogen ions is thought to be a comparatively superior method among known methods.

3,305,365 Patented Feb. 21, 1967 However, even by such a method, there is obtained only a product which is unsatisfactory as regards the recording sensitivity in the primary and secondary exposures, the uniformity of the photographic material itself, the contrast of the image recorded at a writing velocity in a Wide range and the density of the tone of the image. It is still less than completely satisfactory for industrial use as a photosensitive material for direct visual type electromagnetic oscillographic recording paper or the like.

The silver halide emulsion according to the present invention is obtained by adding (1) 10 to mol percent of a cadmium salt, (2) 10 to 25 mol percent of stannous chloride and 3) 0.1 to 10 mol percent thiosernicarbazide per mol of silver to an active gelatin emulsion of silver bromide or silver iodobromide in the presence of excess bromine ions of about 10 to mol percent preferably just before the application of the emulsion onto a support. It is possible to employ a method of adding the cadmium salt in which a part of the amount of the cadmium salt is added in advance in the physical ripening process of the emulsion and the remainder is then added after the second ripening so that the total amount of the cadmium salt added may be within the above mentioned range. However, in such case, the optimum amount of the cadmium salt to be added in the physical ripening process is in the range of 0.1 to 1 mol percent. Above 1 mol percent, the fogging of the background will increase. This is because the functional effect of the cadmium salt added in the physical ripening process will be amplified more remarkably than in the case where it is added just before the application of the emulsion onto a support. If the total amount of 10 to 40 mol percent of the cadmium salt is added only just before the application of the emulsion onto a support and after the second ripening, no fog will be seen to occur.

A feature of the present invention i to add a cadmium salt, stannous chloride and thiosemicarbazide in amounts in the ranges described above in the process of preparing an emulsion. The cadmium salts that can be used include cadmium chloride, cadmium bromide, cadmium iodide and cad-mium nitrate.

As explained below, the present invention comprises a process for producing the above mentioned emulsion and a photographic material made by applying such an emulsion as a layer on a suitable support, such as paper or film. The photographic material of the present invention is useful especially as direct visual type electromagnetic oscillographic recording paper. It is as useful for photographic duplication of various images and recording of X-rays and gamma rays as in the oscillograph. The features of the effects of the present invention are that the visible image obtained with the photographic material of the present invention is a blue black which is very close to black, that its degree of clearness is very high, that the density of the background not subjected to.a high intensity of illumination is very slight, that the image contrast is very high and is very uniform in a wide range of writing velocities and that the writing sensitivity is very high. Thus the writing sensitivity is so high and the image contrast is so uniform and high that the recording of oscillographs is possible in a wide range of writing velocities or in a wide frequency range and it is easy to judge recorded traces. One of the other excellent features is that the photosensitive material according to the present invention is very stable with the lapse of time and can be preserved for a long time. Another excellent feature is that the photosensitive material according to the present invention causes substantially no local fogging of the emulsion due to the pressure effect. The pressure fogging" is a phenomenon of producing photolyzed silver in the part of a local strain caused in silver halide crystals by abrasion due to bending or with a hand or tool in the process of handling the photosensitive material. In practice, it appears on the emulsion surface of printing paper before or after the recording and finally makes it difficult to read the recorded images. I

In the conventional recording paper of this kind, the color of the developed visible image is light brown, blue or purple. It has not been possible to obtain a high density color close to black, as is obtained with the product of the present invention. Also it has not been possible to obtain a high contrast in which the density of the background so highly controlled as is the case with the prodnet of the present invention. That is to say, even if the density of the visible image is made so high as to be close to black with a known conventional emulsion, the density of the background with conventional emulsions will also become so high after the secondary exposure that the contrast will be insufficient and, when many phenomena are to be recorded and judged on the same recording paper, the reading after the recording will be diflicult.

The conventional recording paper of this kind has additional defects, some of which are that it changes during preservation before exposure, loses its characteristic performances in a short time and is apt to become unable to give visible images and that, even if it is used after the production and visible images are obtained, the thus once obtained images will be apt to disappear in a. short time and the time of its preservation is short. On the other hand, a great advantage of the present invention is that the preservation before the use of the photographic material obtained by the present invention and the photodeveloped images after the use of the material are stable for a long time. That is to say, if the product is preserved by intercepting the diffused ambient sun light or any artificial light under the normal preserving conditions, it will be stable without reducing the performances for a long time, such as about 1 to 1.5 years. Further, as the new photographic material of the present invention requires no wet chemical development, it is very convenient to use. In the dry process, just after the recording, the operator can see or use the image.

The new silver halide emulsion of the present invention can be prepared by precipitating silver bromide or silver iodobromide in an aqueous solution containing an active gelatin. Such an emulsion can be prepared by gradually adding an aqueous solution containing a water-soluble silver salt, such as, for example, silver nitrate, to an aqueou solution containing:

(1) potassium bromide or potassium bromide and potassium iodide and (2) an active gelatin.

In preparing silver bromide and silver iodobromide emulsions, bromine ions are added in an amount larger than the equivalent required to react with the silver salt. Prefer-ably an excess of about to 50 mol percent potassium bromide per mol of silver is used. It is desirable to use 0.1 to 1 mol percent potassium iodide together with potassium bromide. In such case, the gelatin to be used must be an active gelatin of a sensitizing type. With the inert gelatin, the sensitizing action will be inhibited and substantially no density of the visible image will appear.

In the preparation of such emulsion, a described above, the feature of the present invention is to add a combination of the three additives, namely the cadmium salt, stannous chloride and thiosemicarbazide in the process of preparing the emulsion. That is to say, 10 to mol percent of a cadmium salt, 10 to 25 mol percent stannous chloride and 0.1 to 10 mol percent thiosemicarbazide per mol of silver are contained in the presence of excess bromine ions of about 10 to mol percent in the emulsion. It is preferable to add these additives just before the application of the emulsion onto a support after the second ripening of the emulsion. However, as mentioned above, it is possible to add the cadmium salt in two stages, one stage being during the physical ripening process and the second stage being just before the application of the emulsion onto the support and after the second ripening. That is to say, it is possible to employ a method wherein 0.1 to 1 mol percent of the cadmium salt per mol of silver is added in advance in the physical ripening process and then the remainder of cadmium salt is added just before the application of the emulsion onto the support and after the second ripening so that the total amount of the cadmium salt added may be 10 to 40 mol percent. The photosensitive material thus obtained by the method wherein a part of the cadmium salt is added in the physical ripening process provides substantially the same performance except that it gives recorded images of a little higher blackness as compared with the material obtained by the method wherein the cadmium salt is added only just before the application of the emulsion onto the support and after the second ripening. In the process where a part of the cadmium salt is added in the physical ripening process, it is preferable to add the cadmium salt to a gelatinpotassium bromide or gelatin-potassium iodide-potassium bromide aqueous solution. When the cadmium salt is contained in the emulsion as mentioned above, a remarkable supersensitizing action will be given to stannous chloride and thiosemicarbazide, the image density and contrast on the recording paper will be increased, the blackening of the background will be cont-rolled even by the irradiation with a fluorescent lamp or the diffused ambient sun light and at the same time the appearance of the visible image will be made faster in a wide frequency range.

In the direct visual type oscillographic recording paper according to the present invention, the image appearing time in the secondary exposure is short. This is the most desirable property in practice. Such recording paper has an advantage of further accelerating the intended recording and judgment of the data.

In the present invention, the optimum range of the ripening temperature for preparing the emulsion is 60:5 C. When the temperature is higher than that, fogging of the emulsion will be apt to occur and the contrast will be lower. When the temperature is lower than that, the ripening will be apt to be insufficient. That is to say, in preparing the emulsion, it is preferable to ripen the emulsion at the above mentioned optimum temperature for at least 20 minutes and more preferable to add an aqueous solution of an active gelatin and carry out a second ripening at the above mentioned optimum temperature for 2 to 10 minutes.

Further, in the present invention, the optimum amount of excess bromine ions is about 10 to 50 mol percent. When the amount of bromine ions used is smaller than that, the fogging of the background will increase. When it is larger than that, the density of the image will be lower and the stability with the lapse of time will be reduced.

Stannous chloride is considered to act as a strong reduction sensitizing agent, to contribute to the increase in the writing sensitivity and to have an action of improv' ing preservability. The action of any of such cadmium salts as cadmium cloride, cadmium bromide, cadmium iodide and cadmium nitrate is substantially the same. It acts mostly as a sensitizing agent but is thought to also have a inhibiting effect and is essential to increase the image contrast by inhibiting the fogging of the background. Especially the cadmium salt has a remarkable influence on the increase of the image density. When it is added together with stannous chloride and thiosemicarbazide, the recorded image will become a blue black which is very close to black. Each of the stannous chloride and the thiosemicarbazide alone has substantial ly no functional effect of blackening the image. The effect of the cadmium salt in the present invention can be said to be especially controlling in increasing the image density and contrast.

There is generally known a method of sensitizing a photographic emulsion specifically having silver chloride as a photosensitive body with a slight amount of a cadmium salt. However, in the case of a silver chlorobromide emulsion of a higher silver bromide content, pure silver bromide emulsion or silver iodobromide emulsion, the addition specifically of a large amount of the cadmium salt will desensitize the emulsion and will be very difiicult to use.

On the other hand, in the present invention, even in the case or a pure silver bromide or silver iodobromide emulsion, when a comparatively large amount of cadmium is used together with stannous chloride and thiosemicarbazide, the sensitizing effect will be obtained. It is thus possible to obtain an excellent photosensitive material which can be used as a direct visual type electromagnetic oscillographic recording paper.

The thiosemiearbazide has an action of making the deposition of photolyzed silver quick and easy as a halogen acceptor. In case it is not added, the image density will decrease and the image contrast will be lost As regards the amounts of addition of the above mentioned additives, when the stannous chloride is less than mol percent, the sensitizing eifect will be very slight. When it is more than 25 mol percent, the sensitizing action will be retained but the emulsion to which it is added will become so acid that the physical properties of the gelatin will be lessened remarkably. Either is undesirable. The optimum amount of addition of stannous chloride is about mol percent mol of silver. When the cadmium salt is less than 10 mol percent, the sensitizing, inhibiting and image blackening effects will be weak. When it is more than 40 mol percent, the increase of the fogging of the background will be remarkable. The optimum amount of the cadmium salt is about 30 mol percent. When thiosemicarbazide is less than 0.1 mol. percent, the decrease of the image density will be remarkable. When it is more than 10 mol percent, after the emulsion is applied, crystals will be apt to be deposited on the support. The optimum amount of thiosemicarbazide is about 5 mol percent. It the above mentioned additives are used respectively individually, it will be impossible to obtain products adapted to use as direct visual type electromagnetic oscillographic recording paper as intended by the present invention. That is to say, only when the above mentioned three kinds of additives are used together in the amounts in the above mentioned ranges, will there be produced an emulsion satisfactory for use to make direct visual type electromagnetic oscillographic recording paper. When a support is coated with such emulsion to make a photosensitive material, excellent performance will be able to be obtained as will be apparent from the following examples.

The present invention shall now be explained with reference to the examples.

EXAMPLE 1 An aqueous solution of an active gelatin containing potassium bromide and potassium iodide was kept at 60 C. to completely dissolve them, Then silver nitrate adjusted to be at 45 C. was dropped into the solution so that the dropping might be completed in minutes. During the dropping, the solution was stirred at a rate of 200 to 250 r.p.m. The solution was ripened for 20 minutes. The second ripening was further carried out at the same temperature for 2 minutes. In such case, the gelatin concentration was adjusted to be 8%. After the completion of the second ripening, the following additives were added to the emulsion in the order and in the amounts mentioned below:

30 mol percent cadmium chloride, 15 mol percent stannous chloride and 5 mol percent thiosemicarbazide per mol of silver nitrate.

The stannous chloride was used as dissolved in an aqueous solution of sorbitol. Then a support was coated with the emulsion so that the amount of silver might be 2.5 to 3.0 g. per 1n. of the support. With this coated material, images were recorded at a writing velocity of 400 m-./sec. at a signal of 2,000 cycles/sec. and an amplitude of 6 cm. under the following exposing conditions:

Primary exposure A direct visual type electromagnetic oscillograph (model EMO1) made by Yokokawa Electric Works, Ltd. (Yokokawa Denki Seisakusho) and using a point light source and a very high pressure mercury vapor was used.

Secondary exposure The material was exposed for 5 minutes at an intensity of illumination of 500 luxes with an apparatus (of a trade name of National FL-100) made by Matsushita Electric Company, Ltd. (Matsushita Denki Sangyo Kabushiki Kaisha). The time for the appearance of recorded images in the secondary exposure of the recording paper was as follows:

Examples of numerical values in the case of testing conventional recording paper under the same conditions are given in the parentheses on the right side in the above table.

The contrast (image density/background density) between the recorded image and the background in a wide range of signals (frequencies) was as follows for respective frequencies:

Signal Contrast 50 cycles 2. 12 (1.95) 100 cyclcs 2.10 (1. 91) 250 cyclcs 2. 06 (1.81) 500 cyc1cs 1. 95 (1. 72-) 600 cycles 1.92 (1. 66) 800 cycles--- 1.89 (1. 86) 1,000 cyclesv 1. 83 (1. 55) 1,300 cycles- 1. 70 (1. 43) 1,500 cycles. 1. 62 (1. 35) 2,000 cycles. 1. 57 (1. 30)

Examples of the case of the conventional product are given in the parentheses on the right side in the above table.

By the way, the value of the practical lowest limit of the contrast was about 1.30 in the case of this apparatus.

The tone of the obtained image was in blue black which was very close to black as compared with the purple or blue of the conventional product.

When the photosensitive material according to the present invention had been forcibly incubated at 50 C. under a relative humidity of for 48 hours, substantially the same results were obtained.

EXAMPLE 2 The process of preparing an emulsion was the same as in Example 1. However, 1 mol percent cadmium chloride was added to a gelatin-potassium bromide or gelatinpotassium iodide-potassium bromide aqueous solution in the physical ripening process of the emulsion. 29 mol percent cadmium chloride was added just before the application after the completion of the second ripening of the emulsion so that the total amount of cadmium chloride might be 30 mol percent per mol of silver. Then stannous chloride and thiosemicarbazide were added to the emulsion in the order and amounts mentioned below:

20 mol percent stannous chloride and mol percent thiosemicarbazide.

The photosensitivity of the photosensitive material obtained by using this coating material was that the image density was a little more blackened than in the material in Example 1 but that the other effects were substantially the same as in Example 1. Even after the incubation test, the same results were obtained.

EXAMPLE 3 The process of preparing an emulsion was the same as in Example 1 except that it was a pure silver bromide emulsion. However, the following additives were added to the emulsion in the order and amounts mentioned below just before the application after the completion of the second ripening:

30 mol percent cadmium chloride, mol percent stannous chloride and 5 mol percent thiosemicarbazide.

The photosensitivity of this coating material was the same as of the material in Example 1 except that the image density was slightly lower than in the material in Example 1.

EXAMPLE 4 The process of preparing an emulsion was the same as in Example 1. However, the following additives were added to the emulsion in the order and amounts mentioned below after the completion of the second ripening:

30 mol percent cadmium iodide, mol percent stannous chloride and 10 mol percent thiosemicarbazide.

The photosensitivity of this coating material was substantially the same as of the material in Example 1 except that the image thickness was slightly higher and the image stability more improved than in Example 1.

EXAMPLE 5 The process of preparing an emulsion was the same as in Example 1, except that the emulsion was a pure silver bromide emulsion containing no silver iodide. After the completion of the second ripening, the following additives were added to the emulsion in the order and amounts mentioned below:

30 mol percent cadmium nitrate, mol percent stannous chloride and 1 mol percent thiosemicarbazide.

The photosensitivity of this coating material was the same as of the material in Example 1 except that the image density was slightly lower than in Example 1.

What we claim is:

1. A photosensitive material adapted for direct visual type electromagnetic oscillographic recording, comprismg:

a support having on at least one surface thereof a layer of a silver halide emulsion selected from the group consisting of silver bromide and silver iodobromide emulsions, said emulsion containing bromine ions in an amout greater than the amount required to react with the silver, said emulsion also containing 10 to 40 mol percent of a cadmium salt, 10 to 25 mol percent stannous chloride and 0.1 to 10 mol percent thiosemicarbazide, per mol of silver in the emulsion.

2. A photosensitive material according to claim 1, in which the amount of bromine ions exceeds the amount required to react with the silver by an amount equal to 10 to 50 mol percent, per mol of silver in the emulsion.

3. A photosensitive material according to claim 1, in which potassium bromide is present in the emulsion in an amount sufficient to provide from 10 to 50 mol percent excess of bromine ions over that necessary to react with the silver, per mol of silver in the emulsion.

4. A photosensitive material according to claim 2, in which the emulsion contains from 0.1 to 1 mol percent potassium iodide per mol of silver in the emulsion.

5. A photosensitive material according to claim 1, in which the cadmium salt is a member of the group consisting of cadmium chloride, cadmium bromide, cadmium iodide and cadmium nitrate.

6. A process for the production of a photosensitive composition adapted for direct visual type electromagnetic oscillographic recording, which comprises:

mixing with (a) an active gelatin, silver halide emulsion containing at least one silver halide selected from the group consisting of silver bromide and silver iodobromide and containing bromine ions in an amount greater than the amount required to react with the silver, (b) 10 to 40 mol percent of a cadmium salt, (c) 10 to 25 mol percent of stannous chloride and (d) 0.1 to 10 mol percent thiosemicarbazide, per mol of silver in the emulsion.

7. A process according to claim 6, in which potassium bromide is present in an amount suflicient to provide from 10 to 50 mol percent excess of bromine ions over that necessary to react with the silver, per mol of silver.

8. A process according to claim 6, in which the cadmium salt, stannous chloride and thiosemicarbazide are added to the silver halide emulsion after ripening of the emulsion and just before the application of the emulsion onto a support.

9. A process according to claim 6, in which from 0.1 to 1 mol percent of the cadmium salt, per mol of silver, is added to the emulsion during the ripening thereof, and the rest of the cadmium salt, the stannous chloride and the thiosemicarbazide is added to the emulsion after ripening of the emulsion is completed and just before the application of the emulsion onto a support.

10. A process according to claim 6, in which 0.1 to 1 mol percent of the cadmium salt is added to the emulsionduring the ripening thereof, following which silver nitrate is added to the emulsion, and the remainder of the cadmium salt, the stannous chloride and the thiosemicarbazide are added after ripening of the emulsion is completed and just before the application of the emulsion onto a support.

References Cited by the Examiner UNITED STATES PATENTS 3,033,678 5/1962 Hunt 961l9 3,033,682 5/1962 Hunt 96-119 3,109,737 11/1963 Scott 96-l l9 NORMAN G. TORCHIN, Primary Examiner.

A. E. TANENHOLTZ, J. H. RAUBITSCHEK,

Assistant Examiners. 

1. A PHOTOSENSITIVE MATERIAL ADAPTED FOR DIRECT VISUAL TYPE ELECTROMAGNETIC OSCILLOGRAPHIC RECORDING, COMPRISING: A SUPPORT HAVING ON AT LEAST ONE SURFACE THEREOF A LAYER OF A SILVER HALIDE EMULSION SELECTED FROM THE GROUP CONSISTING OF SILVER BROMIDE AND SILVER IODOBROMIDE EMULSIONS, SAID EMULSION CONTAINING BROMINE IONS IN AN AMOUNT GREATER THAN THE AMOUNT REQUIRED TO REACT WITH THE SILVER, SAID EMULSION ALSO CONTAINING 10 TO 40 MOL PERCENT OF A CADMIUM SALT, 10 TO 25 MOL PERCENT STANNOUS CHLORIDE AND 0.1 TO 10 MOL PERCENT THIOSEMICARBAZIDE, PER MOL OF SILVER IN THE EMULSION. 